1. Field of the Invention
A reflective mode, magneto-optic spatial light modulator (MOSLM) device has planar electrical conductors which function both as optical mirror surfaces and as the address conductors for random access, selective switching of an associated individual pixel element which is formed from a magneto-optic material that exhibits magnetic domain characteristics.
2. Description of Related Art
In the field of magneto-optic devices, materials that exhibit magnetic domain characteristics, the behavior of such magnetic domains, and the use of these magnetic domain materials in sensing and display devices have been described: see U.S. Pat. Nos. 4,563,236; 4,578,321; and, 4,550,983; all assigned to the same assignee as this invention.
A PRIOR ART form of magnetic domain lens known as the Litton Iron Garnet H Triggered Magneto-optic Device (LIGHT-MOD) 10 is shown by FIG. 1. The LIGHT-MOD.TM. lens 10 has a film layer 12 and a film layer support or substrate material 14. The film layer 12 is a relatively thin layer of magneto-optic material selected to exhibit desired magnetic domain characteristics. Such magneto-optic material can be a ferrimagnetic garnet composition; for example, a bismuth substituted iron garnet. The film support material of substrate 14 can be relatively thick compared to the film layer 12, and is selected to exhibit nonmagnetic and optically transparent characteristics. The material of substrate 14 can have the same single crystal structure as the magneto-optic material of film layer 12. For example, the film support material of substrate 14 can be garnet substrate such as gadolinium gallium garnet (GGG).
The film layer 12 of the PRIOR ART LIGHT-MOD lens 10 has a plurality of geometric elements or "pixels" 16 separated by grooves 18 in a row-and-column orientation as shown by FIG. 1. The geometric elements 16 can be formed by ion beam etching the grooves 18 into the film layer material 12. It is contemplated that the grooves 18 can also be formed using a wet chemical etch process. Each of the geometric elements or pixels 16, are formed from a volume of magneto-optic material sufficient to constrain a single, intrinsic magnetic domain that is bistable, i.e. magnetically reversible. One such magnetic domain physically constrained by a geometric element is schematically represented at 20 by FIG. 1 where the "easy axis" of the magnetic domain 20 is perpendicular to the perspective plane of the drawing.
The LIGHT-MOD lens 10 is a passive device; that is, it requires an external source of illumination. Its operation is non-volatile. Once written, a pattern will remain on the device until it is erased or changed. It is not affected by Earth's magnetic field or normal fields from electric equipment.
The LIGHT-MOD lens 10 operates on the principle of optical Faraday rotation. In one LIGHT-MOD lens, plane polarized light is passed through the magnetized film and its plane of polarization rotated clockwise by positive magnetic polarity, and counterclockwise by negative magnetic polarity. Thus, the magnetic state of the individual magnetic film pixel 16 affects the orientation of the plane of polarization of the light that passes through it.
The PRIOR ART LIGHT-MOD lens 10 as shown by FIG. 1 has a plurality of row and column conductor loops, similar to conductor loops 22 and 24, positioned to act upon each of the geometric elements 16. The row and column conductor loops 22 and 24 are positioned in the grooves 18 between adjacent pixels 16. (For another example of LIGHT-MOD lens, see U.S. Pat. No. 4,550,983 granted Nov. 5, 1985 for MAGNETO-OPTIC DEVICE FOR THE CONTROL OF ELECTROMAGNETIC RADIATION by William E. Ross and assigned to the same assignee.)
The matrix of row and column conductors 22 and 24, as shown by FIG. 1, permit the application of a magnetic field to a selected pixel element or elements by coincident current select; here selected pixel element 28.
An electric current passes through each of the selected conductor loops 22 and 24 in the directions indicated by the arrows. If the magnetic field produced at selected geometric element 28 is the same magnetic polarity as the magnetic domain 20, there is no magnetic reversal of the magnetic orientation of the magnetic domain. Where the magnetic field produced at the selected geometric element 28 is of opposite magnetic polarity to that of the magnetic domain, there is a magnetic reversal of the magnetic domain 20; in essence, magnetic domain reversal at the coincidence of conductor loops 22 and 24. This reversal or switching from one state to the other by coincident current pulses is an addressing technique similar to that used for magnetic core memories. Current pulses as short as 10 nanoseconds and of a peak amplitude of 150 ma can be used. A bias coil surrounding the array can also be used since this aids the switching process completing the magnetic domain reversal to saturation after initiation of the switching action by the conductors. It may also be used for "bulk" erase.
The related application cited above teaches a reflective mode, magneto-optic spatial light modulator (MOSLM.TM.) device having a plurality of individual pixel elements formed from a magneto-optic material and supported by a non magnetic substrate. Both the pixel elements and the substrate are optically transparent to incident electromagnetic radiation, such as light, that passes at least through a selected pixel and is reflected back through the pixel by the planar surface of at least one electrical conductor which is positioned relative to the pixel. The electrical conductor can be one of a respective pair of coincident current select conductors positioned to accomplish a desired complete or partial reversal of the direction of magnetization of the magnetic domain which is physically constrained by the pixel.
Magneto-optic devices, including the reflective MOSLM device of the related application, require a relatively large drive current to complete a desired change in the direction of magnetization in the magnetic domain, and have a separate yet complementary requirement to reduce the magnetic domain switching time.